1. Field of the Invention
The present invention relates to a transparent screen which receives image light projected onto a rear side thereof as viewed from a side thereof which faces a viewer so as to display an image, a projection display device which projects image light onto the rear side of the screen so as to display an image, and a method of condensing control signal light applied to the transparent screen from a remote controller onto a photo detector to receive the control signal light.
2. Description of Related Art
A projection display device is an image display device which consists of a Fresnel lens screen, a diffusion sheet (a diffusion layer), and so on. Unlike a CRT (Cathode Ray Tube) and a PDP (Plasma Display Panel), this projection display device is of non-light-emitting type. The projection display device is provided with, as a projector, an illuminating optical system for guiding light applied from a light source in a predetermined direction, a light valve for applying the light guided by the illuminating optical system, and for adjusting the amount of the light according to an image signal so as to form an image, and a projection optical system for expanding and projecting the image formed by the light valve onto a screen.
Projection display devices include a display device of rear projection type which projects image light onto a rear side of the screen thereof as viewed from a viewer and a display device of front projection type which projects image light onto a front side of the screen thereof as viewed from a viewer. A transparent screen for use in a display device of back projection type, among these projection display devices, includes a Fresnel lens screen for bending image light expanded and projected by a projector toward the viewer, and an image display element for forming an image of the image light from the Fresnel lens screen and for providing an angle of divergence for the image light so as to expand the image light.
There is a remote controller as a means for operating a projection display device by remote control. The remote controller uses a light signal having a wavelength which falls within a wavelength band of infrared rays including visible light rays. Because the Fresnel lens screen of a projection display device has a function of bending image light expanded and projected from a light source toward the direction of the viewer, the Fresnel lens screen also has a function of condensing control signal light from a remote controller applied thereto from the direction of the viewer onto a projector inversely. In other words, by using the Fresnel lens as a condensing lens, the control signal light applied from the remote controller can be condensed onto a photo detector efficiently.
A method of receiving such control signal light applied from a remote controller is disclosed by, for example, the following patent reference 1.    [Patent reference 1] JP,63-2477,A (FIG. 2)
Because conventional projection display devices are constructed as mentioned above, if a Fresnel lens screen functions as a condenser lens which condenses incident light onto the optical axis of an optical system, the Fresnel lens screen can condense control signal light applied from a remote controller onto a photo detector efficiently. However, a problem with a case in which a Fresnel lens screen, which is an eccentric optical system, for use in thin-type projection display devices which have seen in recent years is used is that most of the Fresnel lens cannot guide control signal light applied from a remote controller to a photo detector, and therefore the control signal light applied from the remote controller cannot be condensed onto the photo detector efficiently.